Present invention embodiments relate to an airflow perturbation device and techniques for measuring parameters of respiratory mechanics, and more specifically, for detecting sensitivity of a patient's airway to temperature by measuring respiratory resistance.
The respiratory airways can develop a sensitivity to the cooling that occurs when mouth breathing during exercise. This condition is called exercise-induced asthma (EIA), exercise-induced bronchospasm, or exercise-induced bronchoconstriction. Symptoms of EIA include wheezing, tightness or pain in the chest, coughing, and in some cases, prolonged shortness of breath. Up to 80% of children with asthma have symptoms of HA when they exercise. Cold, dry air inhaled through the mouth during exercise is believed to be the main cause of these symptoms. The smooth muscle bands around the airways are sensitive to these changes in temperature and humidity and react by contracting, which narrows the airway and increases resistance to air flow. Injury to the airways from dehydration can make the smooth muscles progressively more sensitive to changes in temperature of the inhaled air.
Diagnosis of ETA is difficult, and a potential for under-diagnosis exists. In the standard diagnostic procedure, spirometry is used at rest to measure baseline pulmonary function parameters, such as Forced Expiratory Volume (FEV), Forced Expiratory Volume in One Second (FEV1), Maximum Voluntary Ventilation (MVV), Maximum Expiratory Flow Rate (MEF), and others. The patient then undergoes a treadmill or bicycle ergometer exercise session, and the spirometry testing is repeated. These procedures have several disadvantages. First, spirometry is predominantly a test of expiration and EIA symptoms are mostly felt during inhalation; second, spirometric measures only approximate respiratory resistance, which is the true symptom of interest; third, the necessity of an exercise session exposes the patient to the possibility of an unpleasant and potentially dangerous situation.
There are also pharmacological challenge tests, such as the inhalation of methacholine or mannitol used to detect airway sensitivity leading to asthma. These tests have low sensitivity for detection of EIA in athletes and are not recommended as a first-line approach in the evaluation of EIA because of the potential of these drugs to elicit extreme bronchoconstriction and dyspnea. These tests must be conducted under the supervision of a trained technician in a facility with emergency medical care available.